The present invention relates to an EGR cooler used for cooling an exhaust gas recirculation device of an automobile and particularly to those provided with a bypass duct portion for exhaust gas integrally with a casing of the EGR cooler.
A conventional EGR cooler is made of an assembly of a large number of flat tubes or a large number of plates, a large number of fins, a casing and a header, in which cooling water is made to communicate through the casing side and an exhaust gas is made to communicate inside each of the flat tubes or the like. If the temperature of the exhaust gas is at predetermined temperature or less, the gas is not to pass through the EGR cooler, but another bypass passage or a bypass integral with the EGR cooler is provided to be passed.
This is proposed in Japanese Patent Application Laid-Open No. 2004-278351 and Japanese Patent Application Laid-Open No. 2004-257366, for example.
The conventional EGR cooler requires a larger space as a whole when the bypass passage is provided separately.
The EGR cooler in which a part of the casing is used as a bypass passage has a large number of parts, which makes assembling cumbersome. Also, since the exhaust gas communicates only through a part of the casing at bypassing and not in a core portion, there is a fear that the casing is thermally expanded partially by the exhaust gas and a heat stress is applied to its connection portion, which could lead to breakage of a bonded portion.
Then, the present invention has an object to provide an EGR cooler in which the number of parts is small, assembling is easy, and even if a heat stress occurs at a part of the casing, it can be rationally absorbed.
Moreover, the present invention has another object to provide a reliable EGR cooler in which the EGR cooler and a bypass switching valve are integrally assembled and brazed/fixed all together so as to ensure sufficient strength.